1. Field of the Invention
The present disclosure relates to an outer casing and a resin molded article, which are used in electric devices, for example, electric appliances such as thin, lightweight and flat display devices, and common electric components such as resistors and speakers.
2. Description of the Related Art
As flat display devices, liquid crystal displays, organic EL displays, plasma displays and the like are produced in a commercial basis. Since liquid crystal displays and plasma displays in particular are thin and capable of displaying on large screens, they have become widely and commonly used as displays in public facilities and the like, in addition to ordinary households.
In cases of such display devices, molded articles are employed as their outer casings so as to meet design requests and to make them lighter. With these display devices becoming widely used, there is being posed, as a problem, disposal treatment of resin molded articles when spent devices are disposed of.
Recently, attention has been directed to resins (or plastics) which decompose by bacterial action when they are buried in the ground. These resins, which are called biodegradable resins (or plastics), have characteristics of being degraded into water (H2O) and carbon dioxide (CO2) in the presence of aerobic bacteria. Biodegradable resins are in practical use in the field of agriculture and also in practical use, for example, as packaging materials for disposable articles and as materials of compostable garbage bags.
Articles using biodegradable resins, for example, when used in the field of agriculture, may be advantageous also to users because spent plastics do not need to be collected. Further, in recent days, plant-derived resins are also receiving attention in the fields of electronic devices and automobiles. Plant-derived resins are obtained by polymerization or co-polymerization of monomers obtained from plant materials. Plant-derived (or plant-based) resins receive attention as earth-conscious resins, for example, for reasons that they can be produced without relying on petroleum resources, that plants used as raw materials grow absorbing carbon dioxide, and that their combustion calories are generally low and the amount of generated CO2 is small even when their disposal is performed by incineration. Plant-derived resins are generally biodegradable, but do not necessarily need to be biodegradable when considered only from a viewpoint of preventing the depletion of petroleum resources. From this, resins which contribute to environmental protection will include, in addition to biodegradable resins, plant-derived resins which are not biodegradable. Hereinafter, these resins are referred to collectively as “environmental resins”.
At present, resins which are in use as environmental resins are divided into three main classes: those based on poly(lactic acid) (hereinafter, sometimes referred to as “PLA”), on PBS (polybutylene succinate (a copolymeric resin of 1,4-butanediol and succinic acid)), and on PTE (modified polyethylene terephthalate).
Among these resins, PLAs can be produced by chemical synthesis in which sugars generated by plants such as corns or sweet potatoes are used as raw materials, and have a possibility of industrial production. Plastics containing such plant-derived resins are referred to as bioplastics. Particular attention is paid to PLAs because mass production of PLAs has been begun using corns as raw material, and thus there is a desire to develop a technology by which PLAs can be applied not only to applications requiring biodegradation properties, but also to a wide variety of applications.
As methods for improving characteristics of such environmental resins, there were proposed methods by which other components were incorporated into them. For example, JP-A 2002-173583 proposes that synthetic mica is incorporated into PLA in the order of 0.5% to 20% by weight, in order to improve the heat resistance of PLA.
In addition, there was reported the possibility of applying of PLAs to personal-computer outer casings by incorporating kenaf fibers into PLAs (Serizawa et al., “Development of Kenaf-Fiber-Reinforced Poly(lactic acids),” Proceedings of the 14th Annual Meeting of the Japan Society of Polymer Processing, pp. 161-162, 2003). Specifically, it was reported that after molding PLA resins having kenaf fibers incorporated therein, the addition of an annealing step resulted in an improved heat resistance of the PLA resins, thereby leading to a higher possibility of applying PLAs to personal-computer outer casings.